[Improvement] Optimize demo test (#1053)

packages/tag/test/__snapshots__/demo.spec.js.snap

@@ -1,6 +1,6 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
-exports[`renders tag correctly 1`] = `
+exports[`renders demo correctly 1`] = `
 <div>
   <div><span class="van-hairline--surround van-tag">标签</span> <span class="van-hairline--surround van-tag van-tag--danger">标签</span> <span class="van-hairline--surround van-tag van-tag--success">标签</span> <span class="van-hairline--surround van-tag van-tag--primary">标签</span></div>
   <div><span class="van-hairline--surround van-tag van-tag--plain">标签</span> <span class="van-hairline--surround van-tag van-tag--plain van-tag--danger">标签</span> <span class="van-hairline--surround van-tag van-tag--plain van-tag--primary">标签</span>

packages/tag/test/demo.spec.js

@@ -1,4 +1,4 @@
-import Tag from '../';
+import Demo from '../demo';
 import demoTest from '../../../test/demo-test';
 
-demoTest(Tag);
+demoTest(Demo);